Semiconductor devices are used in a variety of electronic applications, such as personal computers and cellular phones, for example. One such semiconductor product widely used in electronic systems for storing data is a semiconductor memory, and a common type of semiconductor memory is a dynamic random access memory (DRAM).
A DRAM typically includes millions or billions of individual DRAM cells arranged in an array, with each cell storing one bit of data. A DRAM memory cell typically includes an access field effect transistor (FET) and a storage capacitor. The access FET allows the transfer of data charges to and from the storage capacitor during reading and writing operations. In addition, the data charges on the storage capacitor are periodically refreshed during a refresh operation.
DRAM storage capacitors are typically formed by etching deep trenches in a semiconductor substrate, and depositing and patterning a plurality of layers of conductive and insulating materials over the substrate in order to produce a storage capacitor that is adapted to store data, represented by a one or zero. Prior art DRAM designs typically comprise an access FET disposed in a subsequently deposited layer, disposed above and to the side of the storage capacitor.
The semiconductor industry in general is being driven to decrease the size of semiconductor devices located on integrated circuits. Miniaturization is generally needed to accommodate the increasing density of circuits necessary for today's semiconductor products. Decreasing the size of DRAM's creates manufacturing challenges.
More recent DRAM designs involve disposing the access FET directly above the storage capacitor, sometimes referred to as a vertical DRAM, which saves space by conserving surface area, and results in the ability to place more DRAM cells on a single chip. In vertical DRAM technology, the access FET is positioned vertically at the upper part of a deep trench.